PNIVERSITY  OF  CALIFORNIA  PUBLICATIONS 

COLLEGE  OF  AGRICULTURE 

AGRICULTURAL  EXPERIMENT  STATION 

BERKELEY,  CALIFORNIA      ' 


PRUNING  YOUNG 
DECIDUOUS  FRUIT  TREES 


BY 
WARREN   P.  TUFTS 


BULLETIN  No.    313 

October,  1919 


UNIVERSITY   OF   CALIFORNIA  PRESS 

BERKELEY 

1919 


EXPERIMENT  STATION  STAFF 

Heads  of  Divisions 

Thomas  Forsyth  Hunt,  Dean. 

Edward  J.  Wickson,  Horticulture  (Emeritus). 

Walter  Mulford,  Forestry,  Director  of  Resident  Instruction. 

Herbert  J.  Webber,  Director  Agricultural  Experiment  Station. 

B.  H.  Crocheron,  Director  of  Agricultural  Extension. 
Hubert  E.  Van  Norman,  Vice-Director;  Dairy  Management. 

James  T.  Barrett,  Acting  Director  of  Citrus  Experiment  Station;  Plant  Pathology. 
William  A.  Setchell,  Botany. 
Myer  E.  Jaffa,  Nutrition. 
Charles  W.  Woodworth,  Entomology. 
Ralph  E.  Smith,  Plant  Pathology. 
J.  Eliot  Coit,  Citriculture. 
John  W.  Gilmore,  Agronomy. 
Charles  F.  Shaw,  Soil  Technology. 
John  W.  Gregg,  Landscape  Gardening  and  Floriculture. 
Frederic  T.  Bioletti,  Viticulture  and  Enology. 
Warren  T.  Clarke,  Agricultural  Extension. 
John  S.  Burd,  Agricultural  Chemistry. 
Charles  B.  Lipman,  Soil  Chemistry  and  Bacteriology. 
Clarence  M.  Haring,  Veterinary  Science  and  Bacteriology. 
Ernest  B.  Babcock,  Genetics. 
Gordon  H.  True.  Animal  Husbandry. 
Fritz  W.  Woll,  Animal  Nutrition. 
W.  P.  Kelley,  Agricultural  Chemistry. 
H.  J.  Quayle,  Entomology. 
Elwood  Mead,  Rural  Institutions. 
H.  S.  Reed,  Plant  Physiology. 
J.  C.  Whitten,  Pomology, 
t Frank  Adams,  Irrigation  Investigations. 

C.  L.  Roadhouse,  Dairy  Industry. 

F.  L.  Griffin,  Agricultural  Education. 
John  E.  Dougherty,  Poultry  Husbandry. 
S.  S.  Rogers,  Olericulture. 
L.  J.  Fletcher,  Agricultural  Engineering. 
Edwin  C.  Voorhies,  Assistant  to  the  Dean. 

Division  of  Pomology 

J.  C.  Whitten  W.  L.  Howard 

A.  H.  Hendrickson  W.  P.  Tufts 

E.  L.  Overholser  G.  L.  Philp 

R.  M.  Amesbury  M.  N.  Wood 

H.  Sevier 


t  In  co-operation  with  office  of  Public  Roads  and  Rural  Engineering,  U.  S.  Department  of 
Agriculture. 


PRUNING  YOUNG  DECIDUOUS  FRUIT  TREES 

By  WAREEN  P.  TUFTS 


INTRODUCTION 

The  economic  conditions  existing  in  California  make  it  incumbent 
upon  the  fruit  grower  to  handle  his  orchard  so  that  it  will  come  into 
profitable  bearing  at  an  early  age.  Pruning  experiments  conducted 
at  the  University  Farm  at  Davis  show  conclusively  that  it  is  unneces- 
sary to  wait  seven  or  eight  years  for  the  first  returns.  For  example, 
when  pruned  by  the  new  method,  providing  soil  and  climatic  con- 
ditions are  favorable,  Japanese  plums  may  be  made  to  bear  a  crate 
of  fruit  to  the  tree  the  third  season  and  two  crates  the  fourth ;  French 
prunes  ten  to  twenty  pounds  of  green  fruit  the  fourth  season ;  and 
Bartlett  pears  a  box  of  fruit  to  the  tree  the  fifth  season.  Likewise, 
with  proper  pruning,  the  other  deciduous  fruits  may  be  brought  into 
bearing  correspondingly  early.  This  early  fruiting,  moreover,  is  not 
inconsistent  with  the  best  development  of  the  tree.  The  trees  which 
have  borne  heavy  crops  on  account  of  the  light  pruning  they  have 
received  are  larger  and  stronger  than  those  trees  receiving  the  heavy 
pruning  which  is  customary  in  the  various  fruit  districts  of  California. 

Pruning  is  commonly  accepted  as  one  of  the  necessary  orchard 
operations.  The  work  is  careful]}7  and  assiduously  carried  out  by 
California  fruit  growers  and  is  one  of  their  most  laborious  and  expen- 
sive practices.  Quite  as  many  systems  or  methods  of  pruning  prevail 
as  there  are  fruit  districts  in  the  state.  Heretofore  actual  experi- 
mental evidence  has  not  been  adequate  to  enable  the  grower  to  deter- 
mine the  relative  merits  of  the  different  methods  and  to  choose  with 
certainty  the  best  practice. 

Many  pruning  experiments  covering  long  periods  of  years  have 
from  time  to  time  been  performed  in  different  parts  of  the  United 
States  and  other  countries.  The  results  of  these  experiments,  however, 
may  not  be  directly  applicable  to  California  orchards.  Furthermore, 
practicalh7  all  published  accounts  of  carefully  conducted  pruning 
investigations  deal  only  with  the  apple.  This  fruit,  although  of  great 
commercial  importance,  comprises  a  comparatively  small  portion  of 
the  total  acreage  devoted  to  deciduous  fruits  in  California.  Finally, 
little  knowledge  based  on  exact  experiments  exists  as  to  the  proper 
pruning  methods  for  such  fruits  as  the  almond,  apricot,  peach,  and 


114  UNIVERSITY    OF    CALIFORNIA EXPERIMENT    STATION 

prune.     It  was  deemed  advisable,  therefore,  to  repeat  many  of  these 
pruning  tests. 

The  Pomology  Division  of  the  University  of  California  has  in 
progress  pruning  experiments  with  almonds,  apples,  apricots,  cherries, 
peaches,  pears,  plums,  prunes,  and  walnuts.  Obviously,  it  will  take 
several  years  to  conclude  these  investigations.  The  results  already 
obtained,  however,  throw  much  light  upon  the  best  methods  of  shaping 
young  trees  in  order  to  bring  them  into  earlier  fruiting  and  to  secure 
larger  and  stockier  trees  in  a  more  economical  way. 

WHAT    IS    PRUNING 

Pruning  is  the  art  of  modifying  the  natural  habit  of  the  fruit  tree 
in  order  to  secure  fruit  in  greater  abundance,  more  regularly,  and  of 
better  quality  than  could  otherwise  be  the  case.  The  cutting  of  a  tree 
is  designed  to  change  its  form,  its  function,  or  both  form  and  function. 
However,  the  physiological  response  of  a  tree  to  any  kind  of  pruning 
is  such  that  it  is  practically  impossible  to  modify  its  shape  without 
at  the  same  time  profoundly  influencing  its  functions. 

Briefly  stated,  the  purposes  of  pruning  are  five-fold : 

1.  To  produce  a  vigorous,  mechanically  strong,  healthy  tree,  free 
from  sunburn,  capable  of  producing  heavy  crops  over  a  long  period 
of  years. 

2.  To  secure  a  tree  well  shaped  for  convenience  and  economy  in 
orchard  management. 

3.  To  distribute  the  fruiting  area  well  over  the  tree. 

4.  To  insure  a  succession  of  profitable  crops. 

5.  To  secure  size  and  quality  of  fruit. 

PURPOSES  OF  PRUNING  YOUNG  TREES 

Promotion  of  Vegetative  Growth* — At  the  end  of  any  growing 
season  the  root  and  top  development  of  a  tree  tend  to  reach  such  a 
balance  that  the  root  system  is  extensive  enough  to  supply  the  top 
with  adequate  moisture  and  mineral  salts  from  the  soil,  and  the  above- 
ground  parts  are  sufficient  to  manufacture  the  complicated  plant  foods 
which  are  necessary  for  the  further  growth  of  the  whole  plant.  When 
a  young  tree  is  dug  from  the  nursery,  with  consequent  loss  of  roots, 
this  balance  is  materially  disturbed.    If  the  top  is  not  cut  back  at  the 


*  A  recent  contribution  by  Kraus  and  Kraybill  (Bull.  149,  Ore.  Agric.  Exp. 
Sta.)  has  shed  much  light  upon  certain  phases  of  the  pruning  question  as  well  as 
other  vexed  horticultural  problems. 


Bulletin  313         PRUNING  YOUNG  DECIDUOUS  FRUIT  TREES  115 

time  of  planting  in  the  orchard,  too  many  buds  will  be  left  to  grow, 
and  the  reduced  root  area  is  unable  to  supply  them  with  adequate 
moisture  and  mineral  matter  from  the  soil. 

This  condition  of  unbalance  will  cause  the  tree  to  die  or  to  make 
but  a  feeble  start.  If,  however,  at  time  of  planting  the  top  is  cut 
back,  each  of  the  remaining  buds  will  have  a  larger  proportionate  share 
of  the  available  moisture  and  mineral  plant  food  materials,  and  the 
subsequent  growth  will  be  more  vigorous.  Chittenden4  has  shown  by 
careful  experiments  covering  this  point  that  poor  growth  invariably 
follows  a  failure  to  prune  back  at  planting.  In  the  case  of  apples 
on  Paradise  stock,  the  set-back  from  non-pruning  at  time  of  planting 
was  noticeable  in  the  three  succeeding  seasons. 

Investigators  working  with  various  horticultural  plants  have,  from 
time  to  time,  used  circumference  of  trunk,  length  of  new  shoot  growth, 
height  and  spread  of  branches,  size  and  weight  of  leaves,  as  proper 
indices  of  the  vegetative  vigor  of  the  plant.  Probably  the  weight  of 
the  entire  plant  top  and  root  is  the  most  accurate  index  of  the  growth, 
taking  into  consideration  not  only  top  but  also  root  elongations,  and 
likewise  increments  to  the  older  portions  of  both  top  and  root. 
Obviously  it  is  impossible  to  take  up  a  tree  at  stated  intervals,  wash 
the  soil  from  its  roots,  weigh,  and  then  expect  that  plant,  when 
replaced,  to  continue  its  development  undisturbed.  It  would  seem 
from  the  measurements  herein  recorded  that  a  definite  correlation 
exists  between  trunk  circumference  and  the  weight  of  both  root  and 
top.  Such  being  the  case,  a  simple  measurement  of  the  circumference 
of  the  trunk  of  the  tree  is  a  fair  indication  of  its  total  development. 

With  the  weighing  and  measuring  of  trunk  circumferences  just 
above  the  crown  of  the  tree  of  241  two-year-old  black  walnut  (Juglans 
Calif orma  var.  hindsii)  seedlings,  245  almond  (Prunus  communis) 
seedlings,  and  215  peach  (Prunus  Persioa)  seedlings,  the  author  has 
been  able  to  calculate  the  correlation  existing  between  root  and  top 
development  as  well  as  the  correlation  existing  between  trunk  cir- 
cumference and  root  and  top  weights.  These  seedlings  received  ordi- 
nary commercial  nursery  treatment,  but  instead  of  being  budded  dur- 
ing the  latter  part  of  the  first  summer  and  then  severely  cut  back 
during  the  dormant  season,  they  were  allowed  to  make  two  seasons' 
undisturbed  growth  in  the  nursery  row.  At  the  end  of  two  years  the 
entire  planting  was  removed.  The  walnuts  were  pulled  with  a  tractor 
soon  after  a  heavy  rain,  with  the  result  that  practically  the  whole 
root  system  was  obtained.  "Walnut  trees  with  broken  tops  or  roots 
were  not  included  in  these  measurements. 


116  UNIVERSITY    OF    CALIFORNIA EXPERIMENT    STATION 

It  was  found  impracticable  to  pull  the  fibrous-rooted  trees  with  a 
tractor;  consequently  as  complete  a  root  system  of  the  peach  and 
almond  was  not  obtained  as  with  the  walnut.  It  is  thought,  neverthe- 
less, that  inasmuch  as  the  root  systems  removed  with  these  trees  were 
as  uniform  as  possible  with  hand  digging,  the  measurements  and 
weights  are  decidedly  worth  while. 

TABLE  1 

Summary*   of  Correlation   Coefficients  Calculated   for   Two-Year-Old 

Seedling  Trees 
Top  Mooted  Plant 

Walnut 

Correlation  betAveen  weight  of  root  and  top 83  ±  .010 

Correlation  between  circumference  of  trunk  and  weight  of  top       .83  ±  .013 

Correlation  between  circumference  of  trunk  and  weight  of  root       .83  ±  .013 

Fibrous  Mooted  Plants 

Almond 

Correlation  between  weight  of  root  and  top 46  ±  .031 

Correlation  between  circumference  of  trunk  and  weight  of  top       .91  ±  .0074 

Correlation  between  circumference  of  trunk  and  weight  of  root       .76  ±  .018 

Peach 

Correlation  between  weight  of  root  and  top 89  ±  .0095 

Correlation  between  circumference  of  trunk  and  weight  of  top       .92  ±  .007 
Correlation  between  circumference  of  trunk  and  weight  of  root       .84  ±  .013 

The  coefficients  just  given  are  high,  and  are  indicative  of  a  very 
close  degree  of  correlation  existing  between  the  circumference  and 
weight  of  the  tree,  both  top  and  root.  With  this  fact  established,  it 
would  seem  that  reliance  may  be  placed  on  the  results  obtained  from 
any  orchard  treatment  influencing  the  growth  of  non-bearing  trees 
when  such  results  are  based  on  trunk  circumference  measurements. 
Attention  is  here  directed  to  the  fact  that  this  form  of  measurement 
takes  into  consideration  only  quantitative  changes  in  the  plant,  and 
pays  no  regard  whatever  to  qualitative  changes.  For  this  reason, 
circumference  measurements  lose  much  of  their  value  as  soon  as  the 
trees  cease  their  purely  vegetative  growth  and  prepare  for  the  pro- 
duction of  blossoms  and  fruit. 

Experiments  devised  to  answer  the  question  as  to  the  results  to  be 
expected  from  light  and  heavy  pruning  of  young  trees  have  been 
conducted  at  the  University  Farm  at  Davis  during  the  past  four 
years.  These  investigations  have  in  large  part  been  preliminary  to  a 
more  thoroughly  detailed  study  of  the  whole  pruning  problem  as  it 
relates  to  California  pomology.     The  results  have  been  so  striking, 


*  For  detailed  discussion,  sec  article  by  author  in  Monthly  Bull.  Calif.  Dept. 
kgrl.,  Vol.  VIII,  No.  9,  Sept.,   1919. 


Bulletin  313         PRUNING  YOUNG  DECIDUOUS  FRUIT  TREES  117 

however,  and  so  much  at  variance  with  common  practices  in  the  state 
that  it  is  thought  best  to  publish  them  at  this  time.  In  most  instances 
the  number  of  trees  involved  in  this  study  has  been  adequate  to  allow 
of  definite  conclusions  being  drawn.  In  a  few  instances  the  number 
of  trees  receiving  identical  treatments  was  relatively  small.  The 
results,  however,  have  in  no  instance  been  contradictory. 

The  fruits  under  experiment  were  the  apricot,  cherry  (sweet), 
peach,  pear,  plum  (Japanese  and  European),  and  prune.  These  trees 
were  planted  in  February,  1915,  on  deep  soils  of  the  Yolo  series  run- 
ning from  fine  sandy  loam  to  clay  loam,  and  have  received  only  one 
irrigation,  and  that  inadequate,  during  one  of  the  four  seasons  they 
have  been  in  the  orchard,  and,  with  the  exception  of  the  pruning 
treatment,  have  received  identical  culture.  The  following  table  brief!}* 
summarizes  the  results  of  the  different  pruning  treatments  after  one 
summer's  growth.  Measurements  were  taken  at  the  beginning  and 
at  the  end  of  the  third  season. 

TABLE  2 
Average  Increase  in  Circumfe:  ence  in  Centimeters 

Pruned  Pruned 

severely.  moderately.  Pruned 

Thinned  and  Thinned  and  lightly. 

Kind  of  fruit                          headed  headed  Thinned 

severely.  moderately.                                   only. 

Apricot    (Boyal)    11.7  cm.  12.6  cm.  15.3  cm. 

Cherry    (Napoleon)    10.0  11.2  12.3 

Peach    (Elberta)    12.0  16.9  19.4 

Pear   (Bartlett) 8.7  9.1  9.7 

Plum  (Japanese— Climax)  ....  6.3  10.4  11.3 

Plum  (European— Pond)  7.2  8.8  9.4 

Prune  (French)   6.2  7.1  8.4 

Average   8.9  10.9  12.3 

Comparable  results  have  also  been  obtained  with  almond  trees 
planted  in  February,  1917. 

In  this  connection  it  is  interesting  to  note  the  results  of  similar 
experiments  conducted  with  the  apple  under  an  entirely  different 
environment.  (The  apple  was  not  included  in  the  plantation  in  which 
the  experiments  above  recorded  were  conducted,  not  being  considered 
a  commercially  important  fruit  in  the  hot  interior  valleys  of  Califor- 
nia). Bedford  and  Pickering,2  at  Woburn,  England,  have  for  many 
years  conducted  pruning  experiments  with  apples.  The  results  of 
these  investigations  show  that  the  less  a  tree  is  pruned  the  larger  and 
heavier  it  becomes.    At  the  end  of  twelve  years  trees  which  had  been 


118  UNIVERSITY    OF    CALIFORNIA EXPERIMENT    STATION 

heavily  pruned,  lightly  pruned,  and  others  which  had  received  no 
pruning  were  dug  up  and  examined.  It  was  found  that  those  trees 
which  had  been  heavily  pruned  during  the  experiment  were  16  per 
cent  lighter  than  those  which  had  received  a  light  pruning  only,  and 
the  trees  which  had  not  been  pruned  at  all  were  20  per  cent  heavier 
than  the  lightly  pruned  ones.  Alderman  and  Auchter,1  in  experiments 
carried  on  for  four  years  in  West  Virginia,  found  that  heavily  pruned 
trees  had  an  average  increased  trunk  diameter  of  1.61  inches,  those 
moderately  pruned  one  of  1.69  inches,  and  those  lightly  pruned  one 
of  1.93  inches.  Likewise,  Gardner5  in  Oregon  found  that,  on  the 
average,  the  unpruned  tree  increases  in  size  a  little  more  rapidly  than 
the  tree  that  is  winter-pruned  only,  or  that  is  both  winter-  and 
summer-pruned.  Attention  should  be  directed  at  this  point  to  the 
fact  that  in  all  these  cases  cited,  measurements  were  made  on  young 
trees  where  the  bulk,  if  not  all,  of  the  plant's  energy  was  being 
expended  upon  wood  growth,  and  little  upon  fruit  production. 
K  A  word  of  explanation  of  the  facts  just  presented  may  not  be 
amiss.  Fruit  growers  have  for  many  years  been  aware  that  the  buds 
toward  the  tip  of  the  shoot  are  the  ones  most  likely  to  put  out  new 
shoot  growth  at  the  first  opportunity.  A  large  per  cent  of  the  total 
plant  food  stored  in  twigs  is  in  the  uppermost  parts.  Magness9  has 
shown  by  defoliation  experiments  that  plant  food  synthesized  in  one 
portion  of  the  tree  is  transported  only  to  a  limited  extent  for  the 
nutrition  of  other  parts  of  the  same  tree.  He  also  points  out  that  the 
larger  the  foliage  area  is  the  better  will  be  the  nutrition  of  adjacent 
parts.  It  is  a  common  observation  that  leaves  are  larger  and  more 
abundant  near  the  tip  of  the  shoot.  Likewise  Chandler3  in  his  studies 
with  sap  concentration  (which  may  be  taken  as  an  index  of  plant  food 
storage)  found  higher  concentrations  in  the  upper  twigs  and  leaves 
than  in  corresponding  parts  lower  down.  Observations  taken  during 
the  dormant  season,  although  closely  following  those  just  noted,  in 
some  instances  showed  a  greater  concentration  of  sap  in  the  trunks 
than  in  the  twigs. 

Bearing  these  facts  in  mind,  it  is  easy  to  account  for  the  greater 
total  growth  of  long-pruned  shoots  than  of  adjacent  shoots  pruned 
short,  and  of  long-pruned  trees  than  of  trees  severely  headed-back. 
We  find  here  also  an  explanation  of  the  greater  formation  of  fruiting 
wood  on  trees  "thinned-out"  as  compared  with  trees  "headed-back" 
(see  page  124).  In  this  connection,  the  fact  must  be  remembered  that 
any  pruning  reduces,-  in  direct  ratio  to  its  severity,  not  only  stored 
food  materials  but  also  the  potential  leaf  area  of  the   plant  which 


BULLETIN  313         PRUNING  YOUNG  DECIDUOUS  FRUIT   TREES  119 

constitutes  the  principal  "machinery"  for  the  manufacture  of  carbo- 
hydrates (a  most  important  group  of  plant  foods)  and  the  building 
up  of  the  more  complex  plant  foods  from  materials  taken  from  the 
soil  by  the  roots. 

Heavy  dormant  pruning  undoubtedly  has  the  tendency  to  restrict 
optimum  root  development.  The  roots  are  incapable  of  carbohydrate 
synthesis  and  are  dependent  upon  the  leaves  and  the  above-ground 
parts  for  their  supply.  If  such  supply  is  limited  by  top  pruning, 
then,  as  an  absolute  consequence,  the  root  system  must  be  limited. 
In  the  experiments  already  noted,  the  writer  has  defintely  shown  that 
a  very  close  correlation  exists  between  parts  above  and  those  below 
ground.  A  large  top  presupposes  a  large  root  system,  and  any  treat- 
ment which  limits  root  development  indirectly,  but  surely,  tends  to 
limit  the  growth  of  stem  and  branches,  since  the  water  and  mineral 
intake  are  quite  as  important  factors  in  growth,  development  and 
fruiting  as  are  the  substances  built  up  or  found  in  the  tops  themselves. 

Formation  of  the  Framework. — Plants  do  not  increase  in  height 
except  through  the  growth  of  buds  and  the  elongation  of  the  terminal 
growing  point.  The  height  of  the  main  trunk  is  determined  when  the 
tree  is  cut  back  at  time  of  planting.  The  term  ' '  height  of  head ' '  will 
in  this  article  have  reference  to  the  distance  existing  between  the 
ground  and  the  lowest  scaffold  limb.  Sufficient  trunk  space  should 
be  left  so  that  at  least  six,  or  better  eight  inches  will  intervene  between 
the  main  scaffold  branches.  This  would  mean  that  if  the  young  tree 
is  arbitrarily  cut  off  at  twenty-four  inches  from  the  ground  and  three 
main  branches  selected,  the  lowest  one  should  stand  from  eight  to 
twelve  inches  from  the  ground.  Personal  preference  will  determine 
the  number  of  main  scaffold  limbs,  but  care  should  be  taken  not  to 
have  too  many.  The  author's  preference  is  for  three.  With  only  two 
main  branches,  there  is  danger  of  splitting.  Four  or  five  main  limbs 
make  it  necessary  to  cut  the  tree  rather  high  at  planting  time  or  else 
take  several  years  to  develop  the  scaffold  branches.  At  five  feet  from 
the  ground,  five  to  seven  main  branches  are  all  that  can  usually  be 
accommodated  without  crowding.  The  pruner  should  have  in  mind 
at  all  times  his  ideal  tree  as  it  will  appear  at  bearing  age,  and  shape 
his  pruning  accordingly. 

The  three  main  branches  selected  should  be  properly  balanced 
around  the  trunk  and  form  equal  angles  of  about  120  degrees  each 
(fig.  1).  Likewise,  these  same  branches  should  be  spaced  up  and  down 
the  trunk  as  above  directed  (fig.  2).  These  primary  scaffolds  should 
be  headed  at  from  fifteen  to  thirty  inches  or  more  from  their  juncture 


120 


UNIVERSITY    OF    CALIFORNIA EXPERIMENT    STATION 


with  the  trunk.  The  severity  of  this  first  heading  is  dependent  upon 
the  total  length  of  new  wood,  its  angle  of  growth,  and  the  formation 
of  lateral  branches  on  current  season's  wood  (as  in  the  case  of  the 
peach).  It  may  be  somewhat  misleading  to  make  general  statements, 
but  it  is  necessary  here  to  give  some  idea  as  to  the  amount  of  heading 
back  the  young  tree  should  receive  at  the  first  dormant  pruning.  The 
greater  the  amount  of  one  year  growth,  the  longer  the  branch  should 
be  cut ;  care  should  be  taken,  however,  to  see  that  the  secondary  branch- 
ing does  not  come  too  high.  The  more  horizontal  the  growth,  the  more 
severe  will  be  the  necessary  heading-back  in  order  to  secure  ease  of 
cultivation.     Trees  forming  branches  on  current  season's  growth  may 


Fig.  1. — Looking  downward  on  a  young  tree,  showing  a  satisfactory  arrange- 
ment of  scaffold  branches  around  the  trunk.  This  will  give  balance  and  symmetry 
to  the  tree. 


be  headed  more  lightly  than  otherwise  because  such  heading,  coming 
as  it  does  above  the  forks  formed  naturally  during  the  growing  season, 
is  not  designed  to  secure  additional  branching,  but  rather  to  form 
proper  angle  and  spread. 

The  common  advice  has  been  to  head  back  these  selected  shoots 
severely  in  order  to  secure  (1)  branching,  and  (2)  stockiness.  As 
usually  practiced  this  advice  defeats  its  avowed  purposes.  If  the 
shoots  are  headed  to  six  or  eight  inches  and  then  an  attempt  is  made 
at  the  second  pruning  to  secure  two  branches  from  each  of  the  three 
main  shoots,  crowding  is  sure  to  take  place,  and  the  result  is  that  in 
nearly  all  cases  only  one  growth  is  ultimately  secured  from  each  of 
the  primary  scaffold  branches. 


Bulletin  313       pruning  young  deciduous  fruit  trees 


121 


The  primary  scaffolds  headed  lightly,  as  above  indicated,  at  the 
end  of  the  first  growing  season  will  allow  sufficient  room  for  the 
secondary  main  branches  to  develop  the  second  summer.  With  such 
fruits  as  the  almond,  apricot,  peach,  and  Japanese  plum  no  further 
heading  is  desirable  (if  sufficient  branch- 
ing and  spread  have  been  obtained  with 
the  one  light  heading)  until  the  tree 
comes  into  full  bearing,  at  which  time 
active  vegetative  growth  is  naturally  re- 
tarded. Under  certain  conditions,  cher- 
ries, pears,  and  similar  fruits  require  one 
or  more  additional  headings  (either  win- 
ter or  summer)  to  form  the  necessary 
framework  and  to  secure  the  desired 
spread.  Varietal  characteristics  largely 
determine  whether  or  not  lateral  branches 
will  be  formed  by  using  only  a  thinning- 
out  system  of  pruning.  The  Bartlett 
pear,  for  example,  under  certain  environ- 
ments throws  laterals  without  heading 
the  new  growth,  but  the  Lincoln  pear 
must  be  headed  to  force  laterals. 

It  has  already  been  pointed  out  in  de- 
tail that  heavy  pruning  will  subdue  and 
light  pruning  will  encourage  total  growth 
in  young  trees.  This  rule  will  find  ready 
application  in  the  maintenance  of  the 
proper  balance  between  various  parts  of 
the  young  tree.  The  upper  shoots  will 
generally  have  a  tendency  to  make  a 
stronger  growth  than  the  lower  branches 
and  must  accordingly  be  cut  more  heavily. 
To  encourage  any  branch  or  portion  of  a 
tree,  therefore,  it  is  essential  to  prune 
such  parts  relatively  lightly  in  compari- 
son with  the  branches  or  parts  with  which 
it  must  compete. 

In  this  same  connection,  attention  must  be  called  to  the  evil  results 
of  even  cutting  (fig.  3).  If  two  shoots  forking  from  the  same  branch 
are  headed  evenly,  the  chances  are  that  they  will  develop  equally,  with 
a  resultant  sharp-angled  crotch  which  is  usually  mechanically  weak. 


Fig.  2. — S  pacing  of 
branches  up  and  down  the 
trunk  must  be  sufficient  to 
secure  mechanical  strength 
and  to  avoid  weak,  debris- 
catching  crotches.  Compare 
fig.  15. 


122 


UNIVERSITY    OF    CALIFORNIA EXPERIMENT    STATION 


On  the  other  hand,  if  the  shoot  which  best  continues  the  general 
direction  of  the  framework  of  the  tree  is  cut  longer  it  will  grow 
strong.  The  second  shoot  will,  as  a  consequence  of  being  cut  shorter, 
develop  into  a  minor  fruiting  branch  with  a  strong,  broad-angled 
crotch  (fig.  4). 

The  relative  stockiness  of  branches  of  trees  headed  severely  as  op- 
posed to  those  headed  lightly  is  quite  well 
shown  by  the  following  measurements : 

A  plot  of  apricot  trees  was  headed 
evenly  at  the  time  of  planting  and  again 
at  the  end  of  their  first  season's  growth. 
At  the  end  of  the  second  season  one-third 
of  these  trees  were  given  a  heavy  pruning, 
one-third  a  moderate  pruning,  and  the  re- 
mainder a  light  pruning  by  thinning  only. 
At  the  end  of  the  third  season  girth  meas- 
urements were  made  of  all  main  branches 
at  a  height  of  three  feet  from  the  ground. 
Those  trees  which  had  been  severely 
pruned  had  an  average  girth  of  main 
branches  of  3.85  centimeters,  those  mod- 
erately pruned  of  4.66  centimeters,  and 
those  lightly  pruned  a  girth  of  5.09  centi- 
meters. The  measurements  were  in  all 
cases  on  limbs  of  the  same  age.  These 
results  are  in  accord  with  experiments 
carried  out  in  Germany,6  England,2  West 
Virginia,1  and  Oregon.5  Inasmuch  as  all 
these  experiments  conducted  under  such 
widely  varying  conditions  yielded  prac- 
tically the  same  results,  no  further  con- 
fidence should  be  placed  in  the  tradition 
that  it  is  necessary  to  cut  severely  in  order 
to  secure  "stockiness.'  It  would  seem 
that  if  mechanical  strength,  whether  to 
uphold  heavy  crops  or  to  resist  the  pres- 
sure of  high  winds,  is  wanted,  this  is  to  be  obtained  most  easily  by  the 
lightest  cutting  compatible  with  good  form  and  branching,  which 
probably  must  be  determined  in  many  instances  by  individual  trial. 
Regulation  of  Time  of  First  Fruiting. — Light  pruning  to  obtain 
larger  and  stronger  trees  goes  hand  in  hand  with  early  fruiting.     On 


Fig.  3. — Equal  develop- 
ment of  branches  and  re- 
sulting sharp-angled,  weak 
crotch  (at  A)  occasioned  by 
even  cutting  at  B. 


Bulletin  313         PRUNING  YOUNG  DECIDUOUS  FRUIT  TREES 


123 


the  contrary,  the  production  of  luxuriant  vegetative  shoot  growth 
induced  by  heavy  cutting  of  the  young  tree,  is  antagonistic  to  the 
bearing  of  fruit.  This  presents  the  question  as  to  the  influence  of 
early  fruiting  upon  the  productive  life  of  the  orchard. 

When  a  deciduous  fruit  tree  has  a  spread  of,  say,  five  feet,  it  can 
with  all  safety  be  allowed  to  fruit,  no  matter  what  its  age.     The  rule 


Fig.  4. — Unequal  development  of  branches  and  mechanically  strong  crotch 
caused  by  uneven  pruning  at  points  A  and  B.  Both  branches  are  of  the  same  age, 
but  are  unequally  developed  because  of  uneven  cutting. 


for  the  fruiting  of  a  young  tree  is  the  same  as  that  governing  the 
digging  of  new  potatoes — "when  they  are  big  enough,  they're  old 
enough." 

Many  growers  definitely  adopt  a  scheme  of  pruning  designed  to 
keep  their  trees  from  fruiting  for  eight  or  ten  years,  and  then  when 
the  time  comes  for  the  orchard  to  produce  profitable  crops  it  quite 
often  refuses  to  respond.  This  behavior  results  from  different  causes. 
In  many  instances,  with  such  fruits  as  the  apple,  pear,  prune,  and 


124  UNIVERSITY    OF    CALIFORNIA — EXPERIMENT    STATION 

cherry,  no  fruit  wood  has  been  allowed  to  develop,  every  spur  having 
been  removed  at  the  annual  pruning,  and  to  expect  fruit  from  orchards 
where  no  attempt  has  been  made  to  develop  a  fruit-spur  system  is  the 
same  as  expecting  a  factory  without  machinery  to  turn  out  a  finished 
product. 

With  the  possible  exception  of  the  peach  and  the  quince,  the 
fruit-spur  system  is  the  machinery  necessary  to  the  production  of 
profitable  deciduous  tree-fruit  crops.  The  promotion  of  the  new  shoot 
growth  by  severe  cutting  likewise  prevents  the  formation  of  fruit 
buds.  Certain  buds  are  potentially  fruit  buds,  only  needing  for  their 
development  sufficient  nourishment.  If,  however,  the  equilibrium 
which  exists  under  normal  conditions  between  root  and  top  is  con- 
stantly disturbed,  all  the  strength  of  the  tree  is  utilized  in  reestab- 
lishing this  balance,  resulting  in  the  non-formation  of  fruit  wood. 
Heavy  cutting  opposes  fruit  production  because,  as  a  result,  plant  food 
is  used  up  in  the  production  of  new  shoots  instead  of  in  the  formation 
of  fruit  buds.  This  luxuriant  growth,  in  turn,  by  its  very  denseness 
robs  of  air  and  sunlight  any  wood  attempting  to  form  fruit  buds  for 
the  following  year.  This  fact  is  illustrated  in  figure  5,  which  shows  a 
French  prune  that,  at  the  end  of  the  second  summer,  was  pruned  by 
heading-back,  and  figure  6  a  similar  tree  which  was  merely  thinned- 
out.  The  former  tree  shows  excessive  vegetative  growth  of  new 
branches  above,  but  lack  of  fruit-spur  development  below;  the  latter 
shows  adequate  vegetative  growth  throughout  and  a  fine  development 
of  fruit  spurs.  The  tree  shown  in  figure  6  bore  a  good  crop  of  fruit 
during  its  fourth  season  in  the  orchard.  The  tree  in  figure  5  cannot 
possibly  produce  until  its  fifth  season,  and  then  it  will  take  several 
years  for  its  production  to  catch  up  with  the  other  tree.  All  this  was 
brought  about  by  the  wrong  pruning  during  only  one  season.  Each 
severe  heading-back  puts  off  profitable  production,  not  only  one  year 
but  in  many  cases  for  several  years.  The  more  years  severe  pruning 
is  given,  the  more  disastrous  will  be  the  results. 

The  terms  "heading-back"  and  "thinning-out"  perhaps  need 
additional  explanation.  If  the  new  wood  of  a  tree  were  given  a  50 
per  cent  heading-back,  it  would  mean  that  the  terminal  half  of  the 
past  season's  growth  had  been  removed  (fig.  76).  A  50  per  cent 
thinning-out  would  mean  that  half  the  total  number  of  year-old  shoots 
had  been  removed  entirely,  the  remaining  half  in  no  way  being  cut 
(fig.  la).  The  terms  " heading-back ';  and  "thinning-out"  are  not 
necessarily  confined  to  the  cutting  of  one  year  wood.     Any  pruning 


Bulletin  313         PRUNING  YOUNG  DECIDUOUS  FRUIT  TREES 


125 


Fig.  5. — Exuberant  wood  growth  on  a  three-year-old  French  prune.     This  tree 
was  cut  back  severely  at  the  end  of  the  first  and  second  seasons. 


126  UNIVERSITY    OF    CALIFORNIA EXPERIMENT    STATION 


Fig.  6. — An  ideal  development  of  fruit  spurs  and  lateral  wood  growth  on  a 
three-year-old  French  prune.  Good  wood  growth  was  made  with  no  heading. 
Note  the  poor  main  crotch  caused  by  selection  of  branches  arising  from  one  point 
on  the  trunk. 


BULLETIN  313         PRUNING  YOUNG  DECIDUOUS  FRUIT   TREES 


127 


which  leaves  a  stub,  no  matter  how  old  the  wood,  may  be  considered 
heading.  In  thinning-out,  either  an  entire  branch  is  removed,  or  else 
the  cut  is  made  to  a  lateral. 

A  simple  mathematical  calculation  shows  that  in  the  formation 
of  a  fruit-spur  system  a  thinning-out  process  is  superior  to  heading- 
back.  The  primary  object  of  heading  is  to  produce  a  certain  amount 
of  new  vegetative  growth.  For  the  sake  of  clearness,  we  will  suppose 
that  a  given  tree  has  two  new  shoots  each  bearing  ten  vegetative  buds. 


Fig.  7. — What  is  meant  by  the  expressions  ' ' thinning-out, ,,(i heading-back, ' ' 
etc.:  a,  an  apple  branch  with  one-year  shoots  ' '  thinned-out "  50  per  cent;  b,  an 
apple  branch  with  one-year  shoots  "headed-back"  50  per  cent;  c,  an  apple  branch 
with  one-year  shoots  "thinned-out"  by  two-thirds;  d,  an  apple  branch  with  one- 
year  shoots  ' '  headed-back ' '  by  two-thirds. 


The  problem  is  proposed  as  to  which  system  of  pruning  will  give  the 
greatest  number  of  spurs,  a  50  per  cent  heading-back,  or  a  50  per  cent 
thinning-out?  In  each  case  ten  buds  remain  after  pruning;  in  the 
former  treatment  these  are  divided  five  on  each  of  the  shoots,  in  the 
latter  all  are  on  one  shoot.  In  the  case  of  the  heading-back,  the  chances 
are  that  at  least  five  of  the  total  ten  buds  on  the  two  growths  will 
throw  out  new  shoots,  with  a  possibility  of  three  other  buds  develop- 


128  UNIVERSITY    OF    CALIFORNIA EXPERIMENT    STATION 

ing  fruit-spurs,  the  last  two  buds  remaining  dormant.  If,  on  the  other 
hand  a  thinning-out  is  given  and  all  ten  buds  remaining  are  on  one 
shoot,  although  varietal  characteristics  here  play  an  important  role, 
the  probability  is  that  these  will  be  divided  somewhat  as  follows :  new 
shoots  two,  spurs  five,  dormant  buds  three.  In  our  pruning  experience 
this  hypothetical  case  is  illustrated  in  each  essential  part  in  every 
kind  of  tree  producing  a  spur  system.  The  need  is  readily  seen  of 
having  clearty  in  mind  the  results  aimed  at  by  any  pruning  system. 
Figure  8  shows  the  influence  of  heading  and  non-heading  upon  the 
formation  of  fruit  spurs. 


EFFECT   OF   SUMMER-PRUNING    YOUNG    TREES 

In  the  abundant  literature  dealing  with  the  various  phases  of 
pruning,  many  references  are  made  to  "summer-pruning."  This 
practice  has  in  nearly  all  instances  been  employed  with  the  end  in 
view  of  increasing  fruitfulness  in  full-bearing  trees.  Considered  from 
such  an  angle,  the  discussion  of  the  adaptability  of  summer-pruning 
to  California  conditions  is  not  pertinent  to  this  article.  The  utilization 
of  summer  cutting  in  the  training  of  the  young  non-bearing  tree  must, 
however,  be  considered,  both  on  account  of  its  importance  and  of  the 
extent  to  which  it  has  been  practiced  during  recent  years. 

Pruning  may  profitably  begin  the  first  summer  the  trees  are  in 
the  orchard.  As  soon  as  the  young  tender  shoots  are  three  or  four 
inches  long,  the  trees  should  be  carefully  examined  and  any  growths 
not  to  be  utilized  in  building  the  main  framework  of  the  tree  pinched 
back.  If  done  at  this  time,  all  of  the  strength  of  the  plant  will  go 
toward  a  heavy  vigorous  growth  in  the  remaining  branches,  which  are 
to  be  permanent.  Quite  often,  by  the  suppression  of  shoots  undesir- 
ably placed,  by  merely  pinching  off  the  tips,  growth  can  be  induced 
where  wanted.  It  is  a  good  plan  to  go  over  the  orchard  about  a  month 
or  six  weeks  after  this  first  thinning  in  order  to  see  that  no  new, 
vigorous,  undesirable  shoots  have  arisen.  In  the  suppression  of  the 
undesirably  placed  growths,  two  or  three  leaves  should  be  left  next 
to  the  trunk  in  order  to  shade  it  and  thus  prevent  sunburn.  Evapora- 
tion from  the  surface  of  these  leaves  cools  the  adjacent  parts,  thus 
opposing  scald  and  drying  out.  (See  page  139.)  The  question  is 
sometimes  raised  as  to  the  advisability  of  heading-back  the  three  main 
branches  during  the  first  summer.  The  best  results  have  been  secured 
by  allowing  them  to  make  an  undisturbed  growth. 

During  the  second  and  succeeding  summers  and  until  exuberant 
wood  growth  is  slowed  down  by  fruiting,  it  is  often  desirable  to  give 


Bulletin  313         PRUNING  YOUNG  DECIDUOUS  FRUIT  TREES 


129 


Fig.  8. — a,  A  two-year-old  prune  branch  which  received  a  heading-back  at  the 
end  of  previous  season.  Note  production  of  shoots  and  lack  of  fruit-spurs,  b, 
A  two-year-old  prune  branch  which  was  not  headed-back  at  end  of  previous  season. 
Note  production  of  fruit-spurs,  together  with  sufficient  amount  of  new  wood. 


130 


UNIVERSITY    OF    CALIFORNIA EXPERIMENT    STATION 


the  vigorously  growing  trees  a  pruning  during  the  early  part  of  the 
season  in  order  to  direct  all  the  energies  of  the  tree  into  those  branches 
which  will  be  retained  as  the  future  framework.  If  the  trees  are 
favorably  located  and  make  a  vigorous  start  the  second  summer,  the 


Fig.  ,9. — A  Nonpareil  almond  tree  at  the  end  of  the  second  growing  season. 
This  tree,  in  addition  to  having  been  thinned-out  and  lightly  headed-back  at  the 
end  of.  the  first  season,  received  a  further  thinning-out  and  heading-back  during 
the  following  May.  Note  the  large  numbers  of  fruit-spurs  formed  on  both  one 
and  two-year-old  wood. 

new  shoots  usually  attain  by  the  middle  of  May  a  length  equal  to  or 
exceeding  that  which  should  be  left  at  the  second  dormant  pruning. 
With  the  long  growing  seasons  which  are  experienced  in  nearly  all 


Bulletin  313 


PRUNING   YOUNG   DECIDUOUS  FRUIT   TREES 


131 


the  deciduous  fruit  growing  sections  of  California,  the  dormant  prun- 
ing usually  performed  during  the  second  winter  may  be  moved  up 
to  the  preceding  May,  with  the  purpose  in  mind  of  obtaining  the 
ordinary  second  and  third  seasons'  shaping  during  the  second  year 


Fig.  10. — The  same  Nonpareil  almond  tree  as  in  fig.  9  after  having  been 
primed .  Note  that  all  the  main  branches  are  formed  and  that  no  further  heading- 
back  is  necessary.  This  tree  should  produce  a  good  crop  during  its  fourth  season 
in  the  orchard. 


of  the  orchard's  life.    Pruning  done  at  this  time  not  only  hastens  the 
training  of  the  tree,  but  also  allows  the  removal  of  many  unnecessary 


132  UNIVERSITY    OF    CALIFORNIA EXPERIMENT    STATION 

shoots,  thus  reducing  to  the  minimum  the  second  dormant  pruning, 
with  consequent  advantages  as  already  mentioned  (page  117).  The 
weight  of  brush  actually  removed  from  prune  trees  at  the  second 
dormant  pruning  was,  on  the  average,  in  the  case  of  trees  receiving 
the  summer-pruning,  0.4  pounds  per  tree,  and  where  no  summer- 
pruning  had  been  practiced,  1.3  pounds  per  tree. 

A  most  important  feature  of  the  summer-pruning  just  outlined  is 
its  influence  on  the  formation  of  fruiting  wood.  Figure  9  shows  a 
Nonpareil  almond  tree  at  the  end  of  the  second  growing  season.  This 
tree,  in  addition  to  having  been  thinned  and  lightly  headed-back  at 
the  end  of  the  first  season,  received  a  further  thinning  and  heading 
during  the  following  May.  Note  the  large  number  of  fruit  spurs 
formed  on  both  one-  and  two-year-old  wood.  Figure  10  shows  the 
same  tree  after  pruning.  No  further  heading-back  is  necessary,  as 
all  the  main  branches  are  already  formed.  An  almond  orchard  pruned 
according  to  this  system  should  produce  a  few  nuts  the  third  season 
and  a  fair  commercial  crop  the  fourth  season. 

Judgment  must  be  exercised  as  to  the  adoption  of  this  system  of 
summer-pruning.  Trees  must  be  grown  under  favorable  soil  and 
moisture  conditions.  If  the  pruning  is  done  early  in  the  season  and 
other  conditions  are  as  outlined,  the  author  can  see  no  reason  why 
an  orchard  under  such  a  pruning  treatment  cannot  be  brought  into 
profitable  bearing  a  year  to  three  years  sooner  than  is  now  the  general 
custom.  Whether  this  early  summer  training  should  be  continued 
during  the  third  and  fourth  summers  depends  upon  the  exuberance 
of  growth  and  the  formation  of  fruit  wood.  If  the  trees  show  no 
indication  of  settling  down  to  fruiting,  and  the  vegetative  growth 
is  so  dense  that  fruit  spurs  on  the  lower  portions  of  the  tree  are 
shaded,  then  summer-pruning,  especially  a  thinning  process,  may 
be  advisable  during  later  years.  Likewise,  if  sufficient  branching 
has  not  been  obtained,  this  early  summer  pruning  may  be  employed 
for  several  seasons,  being  of  special  value  in  securing  "spread"  with 
obstinate  upright-growing  trees,  like  the  sweet  cherry. 

Summer-pruning,  whether  performed  early  or  late  in  the  season, 
exerts  a  marked  influence  on  vigor  as  measured  by  trunk  increments. 
During  the  summer  of  1916  the  writer  subjected  four  blocks  of 
flourishing  two-year-old  trees  consisting  of  apricots,  cherries,  peaches, 
pears,  plums  (Japanese  and  European),  and  prunes,  to  various  treat- 
ments. Block  A  received  no  summer-pruning,  and  the  average 
increase  of  the  trunks  was  7.5  centimeters  (152  trees).  Block  B 
received  a  moderate  thinning-out  and  heading-back  on  May  4,  and 


Bulletin  313        pruning  YOUNG  DECIDUOUS  FRUIT  TREES 


133 


the  average  increase  of  the  trunks  was  6.5  centimeters  (252  trees). 
Block  C  received  a  moderate  thinning-out  and  heading-back  on  May  4 
and  again  on  July  11,  and  the  average  increase  of  the  trunks  was 
5.2  centimeters  (96  trees).  Block  D  received  a  moderate  thinning-out 
and  heading-back  on  August  8,  and  the  average  increase  in  diameter 
of  the  trunks  was  5.4  centimeters  (30  trees.  Only  apricots,  cherries, 
and  pears  in  this  block.) 

From  the  figures  just  presented  it  would  seem  that  summer-prun- 
ing at  any  time  is  devitalizing,  and  that  mid-summer  cutting  is  more 
weakening  than  that  done  during  the  early  part  of  the  season.  It  is 
to  be  further  noted  that  two  comparatively  early  summer-prunings 
were  only  a  little  more  weakening  than  one  given  late  in  the  growing 
period. 

A  moment 's  consideration  of  one  or  two  facts  of  plant  growth  will 
make  clear  the  results  obtained  in  these  summer-pruning  experiments. 
As  previously  stated,  early  summer  growth  is  made  at  the  expense 
of  stored  food  material,  and  to  remove  a  certain  portion  of  the  foliage 
before  these  new  leaves  have  had  an  opportunity  in  turn  to  manu- 
facture and  store  plant  food,  robs  the  plant  to  the  same  extent.  After 
active  shoot  elongation  ceases,  the  plant  turns  its  energies  to  the  manu- 
facture and  storage  of  plant  food  for  the  succeeding  year.  The  later 
a  pruning  is  given  in  the  growing  period  during  which  active  shoot 
elongation  is  taking  place  with  no  corresponding  storage  of  plant  food, 
the  greater  will  be  the  plant's  loss,  provided  such  pruning  is  pro- 
portionately heavy ;  a  50  per  cent  pruning  early  in  the  season  removes 
less  than  a  50  per  cent  pruning  late  in  the  season.  If  the  cutting 
during  the  latter  part  of  the  summer  is  designed  to  give  the  same 
relative  shape  as  results  from  a  pruning  given  during  the  early  part 
of  the  season,  more  wood  must  be  removed  both  by  thinning  and  head- 
ing, especially  if  the  new  branches  are  to  be  secured  at  approximately 
the  same  height  from  the  ground.  Under  the  arid  conditions  existing 
in  many  orchard  sections  of  California,  the  soil  moisture  may  be 
insufficient  to  force  a  vigorous  new  wood  growth  late  in  the  season, 
even  if  such  growth  could  be  properly  matured  before  the  frosts  of 
early  winter.  The  orchardist  practicing  late  summer-pruning  on 
young  trees  may  lose  in  a  two-fold  manner : 

1.  The  leaf  area  of  his  trees  is  reduced  just  as  the  time  of  begin- 
ning of  maximum  storage  of  plant  food  in  fruiting  and  vegetative 
parts ;  and 

2.  As  no  benefits  may  accrue  from  late  summer-pruning,  he  loses 
the  cost  of  the  pruning,  which  is  expensive,  coming,  as  it  does,  during 
the  fruit  harvesting  season  when  labor  is  scarce. 


134 


UNIVERSITY    OF    CALIFORNIA EXPERIMENT    STATION 


In  spite  of  the  reduction  in  vigor  just  noted,  results  from  practical 
applications  of  an  mrly  summer-pruning  seem  to  thoroughly  justify 
the  practice,  providing  the  trees  are  in  a  thrifty  growing  condition 
and  that  the  work  is  done  as  early  as  possible  in  the  growing  season; 


r  ■ ' 
!  so. 


Fig.  1.1. — A  pear  tree  trained  as  a  leader  or  pyramid  type  of  tree. 

in  all  valley  locations  not  later  than  the  first  week  in  June,  and 
preferably  by  the  middle  of  May.  Under  foothill  conditions,  these 
dates  may  perhaps  be  delayed  to  one  or  two  weeks  later  with  safety. 
The  earlier  the  season,  the  sooner  the  pruning  should  be  done. 


BULLETIN  313         PRUNING  YOUNG  DECIDUOUS  FRUIT   TREES 


135 


TRAINING   SYSTEMS 

There  are  three  systems  of  training  fruit  trees : 

1.  Leader  or  pyramid  type  of  tree. 

2.  Delayed  open-center  or  modified-leader  type  of  tree. 

3.  Open-center  or  vase-shaped  type  of  tree. 

Leader  Type. — This  system  was  at  one  time  in  quite  common  use 
in  America,  and  is  still  to  be  found  in  some  of  the  older  orchard 
sections  of  the  east,  as  well  as  in  European  countries.  In  training  a 
tree  by  this  system,  the  topmost  branch  is  encouraged  to  gain  the 
ascendency  (fig.  11),  and  as  time  passes  the  tree  becomes  pyramid- 
shaped,  although,  on  account  of  the  shading  of  upper  branches,  it  is 


Fig.  12. — A  Bartlett  pear  started  as  a  "  modified-leader ' '  type  of  tree.  Note 
that  the  upper  shoot  has  been  pruned  somewhat  longer  than  the  others  in  order 
to  encourage  greater  growth  from  this  limb.     See  figs.  13  and  14. 

difficult  at  times  to  maintain  the  lower  limbs.  This  type  of  tree,  how- 
ever, has  nothing  to  recommend  it  to  the  commercial  orchardists  of 
California,  and  is  simply  mentioned  for  the  sake  of  completeness. 

Delayed  Open-Center*  Type. — Trees  of  this  type  are  occasionally 
seen  in  California,  although  not  to  the  extent  the  system  merits.  At 
the  time  of  the  first  heading-back,  the  topmost  limb  is  left  consider- 
ably longer  than  the  other  scaffold  branches  (fig.  12).  Such  a  pro- 
ceeding results  in  the  strong  growth  of  this  limb  (see  page  122).  At 
subsequent  prunings,  growth  from  this  topmost  branch  must  be  sub- 
dued by  heavy  cutting  and  the  remainder  of  the  tree  allowed  to  thrive 
(fig.  14).  The  reason  for  uneven  cutting  at  first,  followed  by  a 
repression  of  the  favored  part,  is  to  enable  the  grower  to  obtain  a 

*  The  author  is  indebted  to  E.  J.  Kraus  for  this  term. 


136 


UNIVERSITY    OF    CALIFORNIA EXPERIMENT    STATION 


Fig.  13. — The  same  Bartlett  pear  as  in  fig.  12  after  the  second  season 's  growth 
in  the  orchard.  Note  the  vigorous  wood  growth  of  the  entire  tree.  Particular 
attention  is  drawn  to  the  greater  girth  of  the  uppermost  scaffold  which  was  cut 
longer  than  the  others  at  the  first  dormant  pruning,  again  emphasizing  the  fact 
that  greater  stockiness  results  from  lighter  cutting.    See  fig.  14. 


BULLETIN  313         PRUNING  YOUNG  DECIDUOUS  FRUIT  TREES 


137 


Fig.  14. — The  same  Bartlett  pear  tree  as  in  figs.  12  and  13  after  four  seasons' 
growth  in  the  orchard.  Photograph  taken  after  pruning.  Note  strong,  sturdy 
framework  and  symmetry  of  the  tree.  Lower  branches  have  been  permitted  to 
overtake  upper  branches  so  that  tree  is  now  nicely  balanced. 


138  UNIVERSITY    OF    CALIFORNIA EXPERIMENT    STATION 

greater  spacing  of  the  scaffold  branches  on  the  trunk,  the  importance 
of  which  has  already  been  discussed.  Many  varieties  of  the  apple, 
cherry,  pear,  and  European  plum  (including  the  prune)  adapt  them- 
selves particularly  well  to  this  style  of  training.  The  term  "delayed 
open-center"  is  used  advisedly  because  by  the  system  just  outlined  the 
tree  is  opened  out  just  as  is  the  case  with  the  true  open-centered  tree, 
with  the  difference  that  in  the  latter  type  of  pruning  the  open  center 
is  obtained  immediately  at  the  time  of  the  first  heading-back,  but  in 
the  former  case  two  to  three  or  four  years  may  be  necessary.  Never- 
theless, trees  pruned  by  the  two  methods  may  be  expected  to  come  into 
bearing  at  about  the  same  time,  but  with  the  delayed  open-center  tree 
somewhat  stronger  and  better  shaped  than  the  strictly  vase-shaped 
tree. 

Open-Center  Type. — Probably  75  per  cent  or  more  of  the  deciduous 
fruit  trees  in  California  are  of  this  general  type.  It  has  proved 
entirely  satisfactory  when  properly  applied.  The  one  glaring  defect 
of  this  system  has  been  the  encouragement  of  all  scaffold  branches  to 
arise  from  one  point  on  the  trunk,  with  the  formation  of  basin  crotches 
or  "water  pockets'1  (fig.  15),  especially  in  upright-growing  varieties 
such  as  the  French  prune.  Consequent  heart-rot  occurs,  with  breakage 
from  a  heavy  load  of  fruit  when  the  trees  should  be  producing  maxi- 
mum crops.  With  this  system,  branches  arising  from  the  main  trunk 
are  given  equal  encouragement  from  the  first.  The  centers  are  kept 
as  open  as  is  compatible  with  freedom  from  sunburn  of  the  branches. 
The  degree  of  openness  of  the  center  varies  with  the  species,  local 
conditions,  and  the  personal  ideal  of  the  grower. 

HEIGHT    OF    HEAD 

One  of  the  factors  limiting  the  profitable  establishment  of  the 
orchard  under  California  conditions  is  the  height  of  the  head.  The 
lower  the  head,  the  greater  will  be  the  shading  of  the  trunk  and  con- 
sequently the  less  sunburn  or  su.nscald  resulting.  This  point  should 
be  especially  emphasized  for  orchards  planted  in  the  hot  interior 
valleys. 

Whitten11  reports  that  records  taken  during  the  hottest  days  in 
Missouri  showed  the  temperature  of  short  trunks  to  be  several  degrees 
lower  than  that  of  long  trunks,  even  when  the  limbs  of  the  former 
were  spread  upward  to  expose  the  thermometers  equally  to  the  sun's 
rays.  Tall  trunks  exhibited  more  sunscald  than  did  short  trunks  even 
where  the  latter  were  not  shaded. 


BULLETIN  313         PRUNING   YOUNG  DECIDUOUS  FRUIT   TREES 


139 


The  lower  temperature  (and  less  scald)  may  be  explained  on  the 
hypothesis  that  short  trunks  were  cooled  by  readier  and  more  abundant 
passage  of  sap  from  roots  to  closely  adjacent  limbs.  Plants  that  bleed 
(e.g.,  maple  and  grape),  bleed  less  and  less  the  higher  up  they  are 
cut,  and  more  and  more  the  nearer  to  the  roots  the  cut  is  made.7 

In  the  same  experiments  conducted  in  Missouri  it  was  found  that 
where  trunks  were  covered  with  growing  spurs  and  rosettes  of  leaves 
the  temperature  was  lower  than  on  naked  trunks  which  had  no  leaves 


Fig.  15. — The  result  of  selecting  branches  arising  from  one  point  on  the  main 
trunk.  In  this  so-called  water  pocket  note  that  the  entire  blade  of  the  knife  is 
under  water.  This  photograph  is  of  a  ten-year-old  almond  tree.  The  trouble  is 
only  just  beginning,  and  unless  immediate  steps  are  taken  for  its  remedy  the 
usefulness  of  the  tree  will  be  shortened  many  years. 


low  down  to  evaporate  water  and  thus  cool  adjacent  parts.  The  above 
facts  hold  true  even  when  the  two  trees  (one  with  short  and  the  other 
with  long  trunk)  had  similar  branch  growth  higher  up. 

The  removal  of  leaves    (checking  evaporation  near  the   inserted 
thermometer)  caused  a  rapid  rise  of  trunk  temperature  to  8  degrees 


140  UNIVERSITY    OF    CALIFORNIA EXPERIMENT    STATION 

Fahr.,  nearer  the  atmospheric  temperature.*  This  shows  that  evapor- 
ation of  water  through  the  leaves  on  higher  twigs  does  not  cool  the 
trunk  so  much  as  evaporation  from  leaves  on  trunk  or  main  limbs. 

Whitten11  also  states  that  low-headed  as  compared  with  high- 
headed  trees  show  a  more  vigorous  condition,  as  witnessed  by  greater 
trunk  and  root  development.  The  question  is  raised  but  not  answered 
as  to  whether  the  distance  between  top  and  root  may  not  have  a 
distinct  bearing  on  the  nutrition  of  these  parts. 

A  low  head  does  not  necessarily  mean  that  cultivation  close  to  the 
trees  will  be  impossible.  Branches  may  arise  from  near  the  ground 
and  yet  grow  at  such  an  angle  that  close  cultivation  is  practicable. 
With  modern  extension  tools  of  culture  it  is  not  so  necessary  to  keep 
the  spread  of  the  trees  above  the  horses '  heads,  and  every  effort  should 
be  made  to  keep  both  the  height  of  the  head  and  the  spread  of  branches 
as  low  as  is  consistent  with  good  culture.  The  lower  the  tree  the 
cheaper  will  be  the  costs  of  orchard  management.  The  expenses  of 
pruning,  spraying,  thinning,  and  harvesting  vary  directly  with  the 
height  of  the  fruiting  area  above  the  ground. 

Other  advantages  of  a  low  head  are,  less  breakage  from  winds, 
fewer  windfalls,  and,  as  opposed  to  extremely  high  heads,  where  an 
extra  season  is  sometimes  taken  to  grow  additional  trunk,  low-headed 
trees  may  come  into  bearing  sooner. 

The  fact  should  again  be  emphasized  that  pruning  is  only  one  of 
the  factors  limiting  profitable  orchard  productivity.  Careful  pruning 
treatment  cannot  be  expected  to  atoue  for  deficiencies  of  soil  fertility, 
moisture,  or  for  an  unfavorable  climate,  or  otherwise  to  take  the  place 
of  careful  and  intelligent  orchard  management. 


PRACTICAL   SUGGESTIONS    ON   THE    SHAPING    OF   YOUNG    FRUIT   TREES 

Experiments  with  the  training  of  fruit  trees,  performed  under 
California  conditions,  have  not  proceeded  far  enough  to  enable  the 
writer  to  state  definitely  the  way  a  young  orchard  should,  under  all 
circumstances,  be  pruned.  The  recommendations  herewith  presented 
are  not  to  be  taken  as  final,!  but  are  based  on  the  best  information  at 
present  available. 


*  In  one  instance  the  air  temperature  was  103°  F.  The  trunk  temperature 
was  90°  F.,  so  long  as  adjacent  rosette  of  leaves  was  intact.  The  trunk  tem- 
perature rapidly  rose  to  98°  F.  upon  removal  of  the  leaves,  with  the  air  tempera- 
ture remaining  constant  at  103°  F. 

f  It  is  planned,  as  our  experiments  progress,  to  issue  publications  from  time 
to  time  dealing  with  the  pruning  of  particular  fruits. 


Bulletin  313        pruning  YOUNG  DECIDUOUS  FRUIT  TREES  141 

For  the  purpose  of  this  discussion  the  different  deciduous*  fruits 
may  be  roughly  grouped  into  two  classes  according  to  habit  of  growth. 
The  first  class  contains  those  fruit  trees  which  form  side  branches  on 
current  season's  growth;  this  includes  the  almond,  apricot,  peach, 
and  Japanese  plum.  The  trees  of  the  second  class  or  group,  the  apple, 
cherry,  pear,  European  plum  and  prune,  do  not  form  side  branches 
on  the  current  year's  wood.  The  above  grouping  does  not  necessarily 
mean  that  all  trees  in  the  same  class  should  receive  the  same  pruning 
treatment. 

As  a  general  statement  it  may  be  said  that  the  trees  of  the  first 
class  can  be  brought  into  bearing  somewhat  sooner  than  those  of  the 
second  class.  Likewise,  the  formation  of  a  symmetrical  framework 
is  more  quickly  attained  with  trees  in  the  first  class  than  with  those 
in  the  second. 

Pruning  Young  Almonds,  Apricots,  Peaches,  and  Japanese  Plums. 

1.  The  nursery  tree  should  be  cut  at  planting  at  a  height  of  twenty 
to  twenty-four  inches  above  the  ground  (p.  119).  With  the  fruits  of 
this  class  the  head  of  many  of  the  trees  may  be  formed  immediately  at 
planting  time  by  making  use  of  side  branches  formed  in  the  nursery. 
In  case  these  branches  are  unsuitable,  they  should  be  removed.  In 
this  operation  care  should  be  taken  not  to  injure  the  ring  of  tissue 
which  surrounds  the  twig  at  its  juncture  with  the  trunk.  It  is  from 
this  tissue  that  the  so-called  "blind-eyes'1  (adventitious  buds)  give 
rise  to  new  shoots. 

2.  The  young  trees  should  receive  a  coat  of  whitewash  soon  after 
planting,  to  prevent  sunburn  on  the  trunk  (p.  138). 

3.  During  April  the  orchard  should  be  carefully  pruned  and  all 
undesirable  growths  pinched  back  (p.  128). 

4.  At  the  first  dormant  pruning  the  trees  should  be  thinned  to 
three  main  branches,  properly  spaced  (p.  119),  and  these  limbs  cut 
back  lightly  above  the  secondary  branching.  In  other  words,  the  trees 
in  this  group  should  not  be  cut  to  "stubs"  except  when  absolutely 
essential.  Figure  16  shows  a  branch  of  an  apricot  tree  cut  to  a  stub 
at  the  previous  pruning,  and  figure  17  shows  the  same  branch  after 
the  undesirable  branches  have  been  removed.  Attention  is  called  to 
the  pruning  wounds  caused  by  cutting  to  ' '  stubs ' '  and  the  poor  crotch 
resulting.  This  condition  is  largely  obviated  by  cutting  to  laterals 
as  in  figure  18  b. 


*  No  pruning  experiments  have  as  yet  been  conducted  with  the  fig,  pecan, 
persimmon,  and  walnut.  These  fruits  belong  in  general  to  the  second  group  as 
above  described. 


142 


UNIVERSITY    OF    CALIFORNIA EXPERIMENT    STATION 


Fig.  1(5. — A  branch  of  an  apricot  tree  cut  severely  to  a  stub  at  the  preceding 
dormant  pruning.  Compare  fig.  17,  which  sIioavs  the  same  branch  after  pruning. 
Unnecessary  wood  growth  should  have  been  removed  early  in  May  and  little 
pruning  would  have  been  necessary  through  the  winter.  Better  still,  this  branch 
should  not  have  been  cut  back  so  heavily  at  the  previous  pruning. 

5.  During  May  of  the  second  summer  the  trees  are  in  the  orchard, 
all  unnecessary  growth  should  be  "thinned-out. "  If  the  trees  are 
making-  a  vigorous  growth  and  the  desired  spread  and  number  of 
branches  are  not  sufficient  for  the  ultimate  framework,  then  in  addi- 
tion to  the  thinning,  a  "heading-back"  may  be  given  (p.  128). 

6.  At  the  second  dormant  pruning  the  tree  will  need  only  a  thin- 
ning-out (p.  121). 


BULLETIN  313         PRUNING  YOUNG  DECIDUOUS  FRUIT   TREES 


143 


Fig.  17. — The  same  apricot  branch  as  in  fig.  16  after  having  been  pruned.  Note 
the  weak  crotch  and  large  pruning  wounds.  Such  severe  pruning  would  not  have 
been  necessary  if  tree  had  been  cut  lighter  during  preceding  winter  or  else  unneces- 
sary growth  removed  early  in  the  growing  season. 


7.  The  same  treatment  should  be  given  at  the  third  as  was  given 
at  the  second  dormant  pruning. 

8.  Trees  in  this  first  group  handled  as  above  outlined  should 
produce  a  good  commercial  crop  during  the  fourth  season  in  the 
orchard,  and  may  thereafter  be  handled  as  full-bearing  trees. 

9.  All  of  the  above  discussion  presupposes  good  soil  conditions 
and  careful  cultural  treatment. 


144 


UNIVERSITY    OF    CALIFORNIA EXPERIMENT    STATION 


B 


Fig.  18. — a,  Nonpareil  almond  after  one  season's  growth  in  the  orchard.  Head 
was  formed  from  nursery  branches  at  time  of  planting.  Note  good,  strong, 
vigorous  growth,  b,  Same  tree  as  in  (a)  after  pruning.  Note  that  the  tree  was 
thinned-out  and  headed  lightly  to  laterals,  c,  Same  Nonpareil  tree  after  two  sea- 
sons' growth  in  the  orchard.  This  tree  was  thinned  and  headed  lightly  in  May  of 
the  second  summer.  Note  the  large  number  of  fruit-spurs  formed  on  both  one- 
and  two-year-old  wood,  d,  Same  tree  as  in  (c)  after  pruning.  Note  that  all  the 
main  branches  are  formed  and  that  no  further  heading-back  is  necessary.  This 
tree  should  produce  a  good   crop   during  its  fourth   season   in   the  orchard. 


Bulletin  313         PRUNING  YOUNG  DECIDUOUS  FRUIT  TREES 


145 


-■  / 

9,  7 


m        ^m 


Fig.  19. — a,  Apricot  tree  cut  to  a  24-inch  whip  at  planting,  b,  Apricot  tree  with 
head  formed  at  planting  time  from  laterals  formed  in  the  nursery  row.  c,  Apricot 
tree  one  year  old  cut  back  moderately  to  laterals,  d,  Royal  apricot  tree  two  years 
old  after  pruning — thinned-out  only — not  headed-back,  e,  Same  tree  as  in  (d) 
after  one  year 's  growth.  Note  strong,  sturdy  framework  and  vigorous  new  growth. 
/,  Same  tree  as  in  (d)  and  (e)  after  pruning  by  thinning-out  only.  This  tree 
produced  good  crops  during  both  third  and  fourth  summers  it  was  in  the  orchard. 


146 


UNIVERSITY    OF    CALIFORNIA EXPERIMENT    STATION 


Fig.  20. — a,  Peach  tree  after  one  season 's  growth  in  the  orchard — cut  to  a 
whip  at  planting,  b,  Same  tree  as  in  (a)  after  pruning.  Note  heavy  thinning-out 
but  rather  light  heading-back.  Heading-back  was  necessary  to  secure  upright 
branches  near  pruning  cuts,  c,  Peach  tree  after  two  seasons'  growth  in  the 
orchard.  Note  vigorous  shoot  growth,  d,  Same  tree  as  in  (c)  after  pruning. 
Note  heavy  thinning-out  but  no  heading.  Only  those  laterals  left  which  might 
form  desirable  permanent  branches. 


Pruning  Young  Apples,  Cherries,  Pears,  European  Plums  and  Prunes. 

1.  The  nursery  tree  should  be  cut  at  planting  at  a  height  of  twenty 
to  twenty-four  inches  above  the  ground  (p.  119). 

2.  The  young  trees  should  receive  a  coat  of  whitewash  soon  after 
planting  to  prevent  sunburn  on  the  trunk   (p.  138). 

3.  During  April  the  orchard  should  be  carefully  pruned,  the  three 
main  scaffold  branches  being  selected  and  all  undesirable  growths 
being  pinched  back  (p.  128). 


Bulletin  313         PRUNING  YOUNG  DECIDUOUS  FRUIT  TREES 


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£> 


Fig.  21. — a,  Three-year-old  peach  tree  before  pruning — pruned  as  outlined  in 
fig.  20.  Note  sturdy  framework  and  abundance  of  new  wood  growth,  b,  Same 
tree  as  in  (a)  after  pruning — thinned-out  heavily,  c,  Four-year-old  peach  tree 
before  pruning — same  tree  as  in  (a)  and  (&).  This  tree  produced  over  100  pounds 
of  first  quality  fruit  during  its  fourth  season  in  the  orchard.  Note  vigorous  wood 
growth,  d,  Same  tree  as  in  (a),  (b),  and  (c)  after  pruning.  Heavily  thinned-out. 
Note  sturdy  framework  capable  of  holding  up  heavy  crops. 

•4.  At  the  first  dormant  pruning  the  trees  should  be  thinned  to  the 
three  main  branches,  properly  placed  (p.  119),  and  these  limbs  cut 
back  so  that  they  will  be  from  fifteen  to  thirty  inches  or  more  long 
(p.  120). 

5.  During  May  of  the  second  summer  the  trees  are  in  the  orchard, 
all  unnecessary  growth  should  be  "thinned-out."  If  the  trees  are 
making  a  vigorous  growth,  a  "heading-back"  of  the  secondary  scaffold 
branches,  in  addition  to  the  thinning  process  may  be  given.  Under 
favorable  conditions,  this  practice  will  result  in  the  securing  of  the 


148  UNIVERSITY    OF    CALIFORNIA EXPERIMENT    STATION 

usual   second   and   third   year's   shaping   during   the   second    season 
(p.  131). 

6.  With  the  exception  of  all  varieties  of  the  sweet  cherry  and  of 
certain  varieties  of  the  other  fruits  of  this  group,  the  pruning  given 
during  the  second  dormant  season  will  consist  of  a  "  thinning-out ' : 
only. 

"Heading-back"  one-year  branches,  under  most  conditions  and 
in  many  varieties  of  apples,  pears,  European  plums  and  prunes,  will 
have  a  decided  tendency  towards  forcing  all  new  shoot  growth  to  arise 
from  near  the  pruning  cuts.  On  the  other  hand,  if  these  same 
branches  are  not  cut  back,  the  new  shoots,  except  in  certain  varieties, 
will  be  well  distributed  up  and  down  the  previous  year's  growth. 
Notable  exceptions  to  this  rule  are  the  Spitzenburg  apple,  Lincoln 
pear,  and  the  Pond  plum,  which  follow  the  habit  of  the  sweet  cherry, 
in  that  new  shoot  growth  arises  from  the  tip  of  one-year  wood  whether 
this  has  or  has  not  been  headed. 

7.  The  same  pruning  as  that  outlined  for  the  end  of  the  second 
growing  season  should  be  given  during  the  third  dormant  season  and 
until  the  trees  come  into  bearing. 

Prunes  and  European  plums  ma}r  be  expected  to  come  into  profit- 
able bearing  somewhat  sooner  than  apples  and  pears.  The  latter  fruits 
in  general  bear  sooner  than  cherries.  The  question  of  variety  plays  a 
most  important  role  in  determining  the  age  at  which  a  certain  fruit 
may  be  expected  to  reach  profitable  bearing.  For  example,  the 
Wagener  apple  is  noted  for  its  precocious  fruiting,  while  the  Northern 
Spy  is  notoriously  slow  in  reaching  productivity. 

8.  Trees  in  this  second  group,  as  above  designated,  may  be  expected 
to  reach  profitable  bearing  during  the  fourth  to  eighth  season,  and 
should  thereafter  be  handled  as  full-bearing  trees. 

9.  All  the  above  discussion  presupposes  good  soil  conditions  arid 
careful  cultural  treatment. 

SUMMARY 

1.  Young  trees  should  have  their  tops  cut  back  at  planting  in 
order  to 

a.  Balance  the  loss  of  roots  removed  in  digging  from  the  nursery. 

b.  Form  a  low  head  for  future  profitable  orchard  management. 

2.  Sunburn  in  part  may  be  controlled  through  shading,  by  means 
of  low-headed  trees,  and  by  the  cooling  effects  of  evaporation  from 
adjoining  leaves.  Long  bare  trunks  have  higher  temperature  than 
short  trunks. 


BULLETIN  313         PRUNING  YOUNG  DECIDUOUS  FRUIT   TREES  149 

3.  Three  main  "scaffold"  limbs  are  all  that  are  desirable,  and  these 
should  be  spaced  six  to  eight  inches  apart  at  the  points  where  they 
arise  from  the  trunk. 

4.  Nursery  lateral  branches,  if  properly  distributed,  may  be  util- 
ized in  forming  the  head  of  the  tree  at  planting  time. 

5.  Six  main  branches  at  five  feet  from  the  ground  are  sufficient 
for  a  mature  tree. 

6.  After  securing  the  desired  number  of  main  branches,  together 
with  the  proper  spread,  it  is  useless,  except  with  certain  kinds  and 
varieties,  to  head  back  the  young  tree  again. 

7.  Lightly  pruned  trees  have  stockier  and  stronger  branches  than 
heavily  pruned  trees. 

8.  The  more  lightly  a  tree  is  pruned,  the  greater  is  its  development. 

9.  The  storage  of  plant  food  per  unit  of  shoot  growth  is  greatest 
near  the  tip. 

10.  To  lessen  total  growth  in  any  branch  or  part  of  a  tree,  cut 
that  branch  or  part  heavily.  To  increase  the  total  growth  in  any  part, 
prune  that  part  lightly. 

11.  Lightly  pruned  trees  come  into  bearing  from  one  to  three  years 
earlier  than  similar  trees  that  have  been  heavily  pruned. 

12.  Early  bearing  is  not  inimical  to  future  productivity. 

13.  Summer  pruning  is  weakening  and  results  in  somewhat  smaller 
trees.  Under  certain  conditions,  however,  this  practice  may  be  advis- 
able and  may  hasten  profitable  production. 

14.  Early  summer  growth  of  the  tree  (to  approximately  June  15) 
is  made  at  the  expense  of  plant  food  stored  the  preceding  summer. 

15.  After  June  15  the  tree  is  mainly  occupied  in  the  manufacture 
and  storage  of  plant  food  for  the  succeeding  year's  wood  growth  and 
fruit  production. 


150  UNIVERSITY    OF    CALIFORNIA EXPERIMENT    STATION 


LITERATURE  CITED 

i  Alderman,  W.  H.,  and  Auchter,  E.  C. 

1916.  The  Apple  as  Affected  by  Varying  Degrees  of  Dormant  and  Seasonal 
Pruning.     In  W.  Va.  Univ.  Agr.  Exp.  Sta.  Bull.  158,  pp.  1-56. 

2  Bedford,  Duke  of,  and  Pickering,  S.  A. 

1907.     In  Seventh  Eeport,  Woburn  Exp.  Fruit  Farm. 

3  Chandler,  W.  H. 

1914.  Sap  Studies  with  Horticultural  Plants.     In  Univ.  Mo.  Col.  Agr.  Exp. 

Sta.  Eesearch  Bull.  14,  pp.  489-552. 

4  Chittenden,  F.  J. 

1915.  Comparison  of  the  Growth  of  Apple  Trees  Pruned  and  not  Pruned 

in  the  Season  of  Planting.     In  Journal  of  the  Royal  Hort.  Soc, 
vol.  41,  p.  97. 

s  Gardner,  V.  R. 

1916.  Pruning  Investigations.    The  Early  Summer  Pruning  of  Young  Apple 

Trees.    In  Ore.  Agr.  Col.  Exp.  Sta.  Bull.  139,  pp.  3-45. 

e  Goethe,  R. 

1899-1900.  Die  Einwirkung  des  all  jahrlich  ausgefuhrten  Schnittes  auf  das 
Wachstum  der  Baume.  In  Bericht  der  Kgl.  Lehranstalt  fur  Obst- 
Wein-  und  Gartenbau  zu  Geisenheim  am  Rhein,  pp.  18-21. 

7  Jones,  C.  H.,  Edson,  A.  W.,  and  Moese,  W.  J. 

1903.  The  Maple  Sap  Flow.  In  Vt.  Agr.  Col.  Exp.  Sta.  Bull.  103,  pp. 
43-184. 

s  Kraus,  E.  J.,  and  Kraybill,  H.  R. 

1918.  Vegetation  and  Reproduction  with  Special  Reference  to  the  Tomato. 

In  Ore.  Agr.  Col.  Exp.  Sta.  Bull.   149,  pp.  1-90. 

9  Magness,  J.  R. 

1917.  Pruning  Investigations,  Second  Report.     Studies  in  Fruit  Bud  Forma- 

tion.    In  Ore.  Agr.  Col.  Exp.  Sta.  Bull.  146,  pp.  3-27. 

10  Tufts,  W.  P. 

1919.  Influence  of  Heavy  and  Light  Pruning  upon  the  Growth  of  Deciduous 

Fruit  Trees,     In  Monthly  Bull.  Calif.  Dept.  of  Agr.,  vol.  8,  no.  9, 
Sept.,   1919. 

ii  Whitten,  J.  C. 

1919.  An  Investigation  in  Transplanting.  In  Univ.  Mo.  Col.  Agr.  Exp.  Sta. 
Research  Bui.  33. 


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151 


Fig.  22. — a,  One-year-old  prune  tree.  Note  splendid  distribution  of  branches, 
secured  by  pinching  undesirable  growths  in  April  after  planting,  b,  The  same 
tree  as  in  (a)  after  pruning.  Thinned  to  three  scaffold  branches  and  these  headed- 
back  lightly.  Note  spur  left  near  ground  for  shade,  c,  Prune  tree  during  May  of 
second  summer.  Same  tree  as  in  (a)  and  (6).  Note  vigorous  new  shoot  growth. 
d,  Same  tree  as  in  (c)  after  having  received  a  summer-pruning  consisting  of  a 
light  thinning  and  heading. 


Fig.  23. — a,  TVo-year-old  French  prune  tree.  Same  tree  as  in  fig.  22.  Note 
laterals  forced  by  the  summer-pruning;  also  fruit-spurs  on  both  one  -and  two-year- 
old  wood,  b,  Same  tree  as  in  (a)  after  pruning  by  thinning-out.  Note  that  frame- 
work is  complete.  No  need  for  further  heading,  c,  Three-year-old  French  prune 
tree  before  pruning.  Thinned  only  at  second  dormant  pruning.  Note  abundance 
of  new  wood  growth  and  numerous  fruit-spurs,  d,  Same  tree  as  in  (c)  after 
pruning  by  thinning.  This  tree  produced  fifteen  pounds  of  green  fruit  the  fourth 
Beason.  Note  poor  main  crotch  in  this  tree  caused  by  scaffolds  arising  from  one 
point. 


Bulletin  313        PRUNING  YOUNG  DECIDUOUS  FRUIT  TREES 


153 


Fig.  24. — a,  One-year-old  apple  before  pruning — a  good  vigorous  growth.  1), 
One-year-old  apple  after  pruning.  Note  splendid  distribution  of  main  branches. 
c,  Two-year-old  apple  before  pruning,  d,  Two-year-old  apple  after  pruning. 
Thinned-out  and  lightly  headed — in  some  cases  it  might  have  been  advisable  not 
to  head  at  this  time.  This  is  largely  a  matter  of  varietal  characteristics,  e,  Three- 
year-old  apple  before  pruning — note  good,  vigorous  growth.  /,  Three-year-old 
apple  after  pruning — thinned-out  only.  A  good  strong  framework  is  already 
formed. 


